The Trump administration is taking the highly unusual step of suing a drugmaker. Specifically, the Department of Health and Human Services has filed a lawsuit against Gilead Sciences. The issue is patent infringement. HHS says Gilead has been infringing on its patents for PrEP. This is a drug regimen that prevents HIV infection.

All right. To help us understand all this, we're going to bring in NPR health policy reporter Selena Simmons-Duffin. Hi, Selena.

SELENA SIMMONS-DUFFIN, BYLINE: Hi.

KELLY: What exactly is PrEP?

SIMMONS-DUFFIN: So PrEP stands for pre-exposure prophylaxis. It's recommended for people who are at high risk for HIV infection. There are only two drugs currently approved for this, and both of them are made by Gilead. Truvada is the one that's been used for PrEP since 2012 - very few side effects. It's a daily pill. It's almost 100% effective in preventing HIV infection.

But only a fraction of the 1 million people who are at risk for getting HIV are on it. And a big part of that - the reason for that is the price. So the list price here is $1,800 a month. A generic overseas is about $6 a month.

KELLY: Wow. OK.

SIMMONS-DUFFIN: So - yeah. Gilead maintains it invented Truvada. It spent about a billion dollars on R&D. But the CDC worked on developing the PrEP regimen, too, with taxpayer money. So there's an activist group called PrEP for All that has been calling for months on the government to defend its patents. And last night with this lawsuit, it seems like the Trump administration is doing what these activists wanted.

KELLY: So they must be over the moon. I'm guessing...

SIMMONS-DUFFIN: Yeah.

KELLY: ...The reaction has been positive.

SIMMONS-DUFFIN: Very, very pleased; also very surprised. One activist I talked to today said it seemed like they'd been screaming into the void about this, but maybe someone was actually listening.

KELLY: And why is the government - what have they indicated about why they were listening now, and what's their argument?

SIMMONS-DUFFIN: So this complaint is very strongly worded. I'm going to - here - read part of it to you. Gilead's conduct was malicious, wanton, deliberate, consciously wrongful, flagrant and in bad faith.

So basically, in general, HHS has lots of patents - thousands of patents. And usually, what happens is they license these patents out to companies and get paid royalties. Gilead didn't do that. So the Financial Times did an analysis over the summer that Gilead owes the government about a billion dollars in royalties. And this complaint asks for enhanced damages, so they could be getting a lot more than that.

KELLY: I'm trying to situate this in terms of where we are as a country with the HIV epidemic because the Trump administration set that goal - right? - that they were going to try to end the HIV epidemic by 2030. Is this a piece of that?

SIMMONS-DUFFIN: Yeah. I think that the HHS is - been trying to reach that goal, and having Gilead set this very high price for this drug that they need to use to get the epidemic to stop has been a frustration. And I think that HHS and Gilead have been negotiating in good faith, it seems like. And this strongly worded lawsuit makes it seem like the government had enough. So just to remind everybody where we are in this epidemic, 40,000 people still get HIV infections every year here in the U.S.

KELLY: New infections every year.

SIMMONS-DUFFIN: New infections every single year. And you know, this is a beginning of a lawsuit. It's a court process. It might take a really long time to sort out, but activists I talked to today think that it could be leverage to get actual concessions from Gilead, and they're really hopeful that that may happen.

KELLY: And real quick - statement from Gilead today.

SIMMONS-DUFFIN: So Gilead maintains that it thinks that HHS's lawsuits are invalid.